The present invention relates to the active monitoring of leakage current to detect potential fault conditions and provide early warning of future potential fault conditions and/or leakage current measurements that exceed defined threshold settings. More specifically, the present invention relates to a leakage current monitoring service and the implementation and operation thereof to provide said detection and early warning.
Electrical systems and devices are generally designed with various precautions in mind. These precautions typically fall into one of two categories: prevention of occurrences of hazardous or undesired events (e.g., by product testing, insulating energized electrical components from nearby conductive surfaces, controlling failure modes, using devices with overload protection, designing for durability, conducting regular maintenance, etc.), or mitigation of the consequences when hazardous or undesired events occur (e.g., by employing system shut down modes). Recently, said design efforts have been focused on addressing the presence of leakage current in electrical systems.
In the current state of the art, mitigation efforts have been addressed by the design and use of ground fault circuit interrupters (GFCIs); GFCIs are most commonly known for use in household outlets and 120 volt AC circuits. GFCIs mitigate the effects of high leakage current (also known as fault current) by disconnecting power to the entire electrical circuit when an upper limit is reached; this upper limit is predefined according to governing codes (see, for example, UL-943, UL-943C, IEC 60364, and IEC 60479). While GFCI devices are in wide use for low voltage systems, their use has not yet been made integral to equipment-grounded high voltage systems. Further, there are some drawbacks to using a traditional GFCI as a leakage current mitigation device. For example, GFCIs will terminate power to the circuit regardless of the condition that caused the fault even if a fault condition has not actually occurred (e.g., a GFCI may terminate power to a lamp circuit during lamp startup, despite the fact that the increase in leakage current is normal for that combination of system and lamp condition). To address this limitation in home electrical circuits, the National Electric Code (NEC) requires that lighting circuits be wired to a separate circuit than the outlets being protected with GFCIs; this ensures the lights will not go out if the GFCI trips. However, this does not address the situation in which the lighting circuit is the circuit being protected by a GFCI-type device, nor does this provision address the need for a warning that the circuit will be interrupted.
In terms of preventative efforts—particularly for high voltage systems—little has been done regarding leakage current. There are commercially available systems which provide instantaneous leakage current measurements, but these devices do not allow for practical recurrent testing. For example, measurements completed at the time of installation of an electrical system may verify proper operating conditions; however, leakage current may increase over the life of the electrical system due to various reasons (e.g., degradation of the wire insulation over time) and thus, will not be reflected in the initial measurement. Trained personnel could return to the site periodically to measure leakage current, but this may not only be cost-prohibitive and time-consuming, but does not ensure the integrity of the electrical system between site visits.
One example of a commercially available device is the SUPERINTEND™ system available from Neel Industrial Systems Pvt. Ltd., Mumbai, India which uses current measuring devices and a local monitoring unit with display screen to capture the data. This particular system has an optional feature that will send current data to a local computer for viewing; however, local staff familiar with such data must be available to interpret the current measurements and decide on a course of action.
The art would benefit from means and methods of continuously monitoring leakage current in an electrical system and intervening before the use of mitigating devices—such as the aforementioned GFCIs—is necessary. The art would further benefit if such means and methods could be made available for many types of electrical systems (including equipment-grounded high voltage systems) and in a manner that does not require excessive oversight (e.g., interpreting data) or participation (e.g., operating measuring devices) from the user (e.g., owner, operator) of the electrical system. Thus, there is room for improvement in the art.